Physical Mechanisms for the Variable Spin-down of SGR 1900+14

We consider the physical implications of the rapid spindown of Soft Gamma Repeater 1900+14, and of the apparent "braking glitch", \Delta P/P = l x 10^-4, that was concurrent with the Aug. 27th giant flare. A radiation-hydrodynamical outflow associated with the flare could impart the required torque, but only if the dipole magnetic field is stronger than ~ 10^14 G and the outflow lasts longer and/or is more energetic than the observed X-ray flare. A positive period increment is also a natural consequence of a gradual, plastic deformation of the neutron star crust by an intense magnetic field, which forces the neutron superfluid to rotate more slowly than the crust. Sudden unpinning of the neutron vortex lines during the August 27th event would then induce a glitch opposite in sign to those observed in young pulsars, but of a much larger magnitude as a result of the slower rotation. The change in the persistent X-ray lightcurve following the August 27 event is ascribed to continued particle heating in the active region of that outburst. The enhanced X-ray output can be powered by a steady current flowing through the magnetosphere, induced by the twisting motion of the crust. The long term rate of spindown appears to be accelerated with respect to a simple magnetic dipole torque. Accelerated spindown of a seismically-active magnetar will occur when its persistent output of Alfven waves and particles exceeds its spindown luminosity. We suggest that SGRs experience some episodes of relative inactivity, with diminished spindown rates, and that such inactive magnetars are observed as Anomalous X-ray Pulsars (AXPs). The rapid reappearence of persistent X-ray emission following August 27 flare gives evidence against accretion-powered models.Comment: 24 pages, no figure

Measuring the use of information and communication technologies (ICTs) in the classroom

In 2003, the ICT Curriculum Integration Performance Measurement Instrument was developed from an extensive review of the contemporary international and Australian research pertaining to the definition and measurement of ICT curriculum integration in classrooms (Proctor, Watson, & Finger, 2003). The 45-item instrument that resulted was based on theories and methodologies identified by the literature review. This paper describes psychometric results from a large-scale evaluation of the instrument subsequently conducted, as recommended by Proctor, Watson and Finger (2003). The resultant 20-item, two-factor instrument, now called Learning With ICTs: Measuring ICT Use in the Curriculum is both statistically and theoretically robust. This paper should be read in association with the original paper published in Computers in the Schools (Proctor, Watson & Finger, 2003) that described in detail the theoretical framework underpinning the development of the instrument

Discovery of Pulsed X-ray Emission from the SMC Transient RX J0117.6-7330

We report on the detection of pulsed, broad-band, X-ray emission from the transient source RX J0117.6-7330. The pulse period of 22 seconds is detected by the ROSAT/PSPC instrument in a 1992 Sep 30 - Oct 2 observation and by the CGRO/BATSE instrument during the same epoch. Hard X-ray pulsations are detectable by BATSE for approximately 100 days surrounding the ROSAT observation (1992 Aug 28 - Dec 8). The total directly measured X-ray luminosity during the ROSAT observation is 1.0E38 (d/60 kpc)^2 ergs s-1. The pulse frequency increases rapidly during the outburst, with a peak spin-up rate of 1.2E-10 Hz s-1 and a total frequency change 1.8%. The pulsed percentage is 11.3% from 0.1-2.5 keV, increasing to at least 78% in the 20-70 keV band. These results establish RX J0117.6-7330 as a transient Be binary system.Comment: 17 pages, Latex, aasms, accepted for publication in ApJ Letter

Validation of a Sapphire Gas-Pressure Cell for Real-Time In Situ Neutron Diffraction Studies of Hydrogenation Reactions

A gas-pressure cell, based on a leuco-sapphire single-crystal, serving as a pressure vessel and sample holder, is presented for real time in situ studies of solid-gas hydrogenation reactions. A stainless steel corpus, coated with neutron absorbing varnish, allows alignment for the single-crystal sample holder for minimizing contributions to the diffraction pattern. Openings in the corpus enable neutron scattering as well as contactless temperature surveillance and laser heating. The gas-pressure cell is validated via the deuteration of palladium powder, giving reliable neutron diffraction data at the high-intensity diffractometer D20 at the Institut Laue-Langevin (ILL), Grenoble, France. It was tested up to 15.0 MPa of hydrogen pressure at room temperature, 718 K at ambient pressure and 584 K at 9.5 MPa of hydrogen pressure

A balloon-borne imaging gamma-ray telescope

A balloon-borne coded-aperture gamma-ray telescope for galactic and extragalactic astronomy observations is described. The instrument, called Gamma Ray Imaging Payload (GRIP), is designed for measurements in the energy range from 30 keV to 5 MeV with an angular resolution of 0.6 deg over a 20 deg field of view. Distinguishing characteristics of the telescope are a rotating hexagonal coded-aperture mask and a thick NaI scintillation camera. Rotating hexagonal coded-apertures and the development of thick scintillation cameras are discussed

Visualizing Information on a Sphere

We describe a method for the visualization of information units on spherical domains which is employed in the banking industry for risk analysis, stock prediction and other tasks. The system is based on a quantification of the similarity of related objects that governs the parameters of a mass-spring system. Unlike existing approaches we initialize all information units onto the inner surface of two concentric spheres and attach them with springs to the outer sphere. Since the spring stiffnesses correspond to the computed similarity measures, the system converges into an energy minimum which reveals multidimensional relations and adjacencies in terms of spatial neighborhoods. Depending on the application scenario our approach supports different topological arrangements of related objects. In order to cope with large data sets we propose a blobby clustering mechanism that enables encapsulation of similar objects by implicit shapes. In addition, we implemented various interaction techniques allowing semantic analysis of the underlying data sets. Our prototype system IVORY is written in JAVA, and its versatility is illustrated by an example from financial service providers

The challenging optics of XtremeD – a neutron diffractometer for high pressures and magnetic fields at ILL developed by Spain

6 páginas, 3 figuras.The Spanish community of neutron scatterers and the ILL are considering the construction of a CRG "extreme conditions Diffractometer (XtremeD)" for both single crystals and powders, operating at high pressures (up to 50 GPa) and high magnetic fields (up to 15 Tesla). High pressure studies require reduced sample volumes. This makes the focusing optics a crucial part of the instrument, in order to have increased flux and to avoid the scattering from the sample environment. The different solutions at different levels of the instrument, which are being studied, will be discussed in this paper.Peer reviewe

Timing Noise in SGR 1806-20

We have phase connected a sequence of RXTE PCA observations of SGR 1806-20 covering 178 days. We find a simple secular spin-down model does not adequately fit the data. The period derivative varies gradually during the observations between 8.1 and 11.7 * 10^-11 s/s (at its highest, ~40% larger than the long term trend), while the average burst rate as seen with BATSE drops throughout the time interval. The phase residuals give no compelling evidence for periodicity, but more closely resemble timing noise as seen in radio pulsars. The magnitude of the timing noise, however, is large relative to the noise level typically found in radio pulsars. Combining these results with the noise levels measured for some AXPs, we find all magnetar candidates have \Delta_8 values larger than those expected from a simple extrapolation of the correlation found in radio pulsars. We find that the timing noise in SGR 1806-20 is greater than or equal to the levels found in some accreting systems (e.g., Vela X-1, 4U 1538-52 and 4U 1626-67), but the spin-down of SGR 1806-20 has thus far maintained coherence over 6 years. Alternatively, an orbital model with a period P_orb = 733 days provides a statistically acceptable fit to the data. If the phase residuals are created by Doppler shifts from a gravitationally bound companion, then the allowed parameter space for the mass function (small) and orbital separation (large) rule out the possibility of accretion from the companion sufficient to power the persistent emission from the SGR.Comment: 11 pages, accepted for publication in ApJ Letter